1. Field of the Invention
This invention relates generally to radiation collimator devices and is concerned more particularly with an X-ray collimator devices having a simplified and compact arrangement of shutter elements.
2. Discussion of the Prior Art
An X-ray generator usually comprises an oil-filled housing having therein an X-ray tube provided with an electron-emitting cathode and a spaced anode target. The cathode generally is disposed to direct a beam of electrons onto a small area, known as the "focal spot" area, of the anode with sufficient energy to generate X-rays in the target material. As a result, X-rays radiate from the focal spot area in all directions within the tube envelope. The useful portion of these X-rays pass, in the form of a conical beam, through an X-ray transparent window of a radially aligned port which is recessed in the wall of the housing. Thus, the focal spot area of the anode target ideally functions as a point source of the conical X-ray beam emanating from the port of the X-ray generator.
The X-ray beam may be directed, for example, through a selected region of a human patient for a limited interval of time, and impinge on an aligned surface area of a rectangular film. However, in order to protect the patient from over-exposure to X-radiation, it is required that the irradiated region of the patient be no larger than the effective area of the rectangular film. Accordingly, there may be mounted over the port of the X-ray generator a collimator device having therein suitable X-ray absorbent shutter elements for providing an adjustable exit aperture of the desired size. In this manner, the conical X-ray beam emanating from the port of the X-ray generator may be restricted by the collimator shutter elements to the proper cross-sectional size and configuration for conforming to the effective area of the rectangular film.
Some X-ray collimator devices of the prior art have a rectangular exit aperture defined by two orthogonally disposed pairs of opposing pivotal shutter plates. However, one pair of shutter plates is mounted for opposing pivotal movement in a plane above the other pair of shutter plates. Also, each of the orthogonally disposed pairs of shutter plates may require relatively complex drive means for adjusting the respective elements of each pair to provide desired aperture sizes. Consequently, the device having the shutter plates and required drive gearing, including entrance shutter-to-exit shutter linkages, may not lend itself to compactness or economy for situations where a compact and relatively inexpensive collimator is desired.